U.S. patent application number 11/706899 was filed with the patent office on 2008-08-14 for composition and method of preparing nanoscale thin film photovoltaic materials.
Invention is credited to R. Douglas Carpenter, Kevin D. Maloney.
Application Number | 20080190483 11/706899 |
Document ID | / |
Family ID | 39684807 |
Filed Date | 2008-08-14 |
United States Patent
Application |
20080190483 |
Kind Code |
A1 |
Carpenter; R. Douglas ; et
al. |
August 14, 2008 |
Composition and method of preparing nanoscale thin film
photovoltaic materials
Abstract
A photo-absorbing layer for use in an electronic device; the
layer including metal alloy nanoparticles copper, indium and/or
gallium made preferably from a vapor condensation process or other
suitable process, the layer also including elemental selenium
and/or sulfur heated at temperatures sufficient to permit reaction
between the nanoparticles and the selenium and/or sulfur to form a
substantially fused layer. The reaction may result in the formation
of a chalcopyrite material. The layer has been shown to be an
efficient solar energy absorber for use in photovoltaic cells.
Inventors: |
Carpenter; R. Douglas;
(Tustin, CA) ; Maloney; Kevin D.; (Newport Beach,
CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET, FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
39684807 |
Appl. No.: |
11/706899 |
Filed: |
February 13, 2007 |
Current U.S.
Class: |
136/256 ;
257/E31.027; 419/38; 420/591; 428/546 |
Current CPC
Class: |
B22F 7/04 20130101; H01L
31/0322 20130101; Y02E 10/541 20130101; Y02P 70/50 20151101; B22F
3/1035 20130101; H01L 31/0749 20130101; Y02P 70/521 20151101; Y10T
428/12014 20150115 |
Class at
Publication: |
136/256 ; 419/38;
420/591; 428/546 |
International
Class: |
H01L 31/0216 20060101
H01L031/0216; B22F 3/10 20060101 B22F003/10 |
Claims
1. A photovoltaic cell comprising: a photon-absorbing layer
comprising metal alloy nanoparticles substantially fused together,
the nanoparticles comprising the formula
Cu.sub.1In.sub.1-xGa.sub.x, where x ranges from 0 to 1, said layer
having been prepared by heating the nanoparticles sufficiently to
permit reaction with material comprising either selenium and/or
sulfur; an electrically conductive substrate supporting the
photon-absorbing layer and providing at least a portion of an
electrical circuit in combination with said photon-absorbing layer;
an emitting layer comprising material capable of absorbing
electrons from the photon-absorbing layer; and an anti-reflective
coating comprising material suitable for permitting a significant
amount of sunlight that strikes the cell to reach the
photon-absorbing layer.
2. The photovoltaic cell of claim 1, further comprising an
environmental protection layer to reduce environmental degradation
of the cell during use.
3. The photovoltaic cell of claim 1, wherein the layer is less than
about 1 micron.
4. The photovoltaic cell of claim 1, wherein the layer is less than
about 500 nanometers.
5. The photovoltaic cell of claim 1 wherein the anti-reflective
coating comprises zinc oxide.
6. The photovoltaic cell of claim 1, wherein the emitting layer
comprises cadmium sulfide.
7. The photovoltaic cell of claim 2, wherein the environmental
protection layer further comprises glass having a low iron
content.
8. The photovoltaic cell of claim 1, wherein a substantial portion
of the nanoparticles are less than about 50 nanometers.
9. The photovoltaic cell of claim 1, wherein the photon-absorbing
layer comprises nanoparticles created using a vapor condensation
process.
10. A method of preparing an electronic device, the method
comprising: mixing on an electrically conductive substrate
particles comprising at least one element selected from Groups VA
and/or VIA with metal alloy nanoparticles made from a vapor
condensation process; and heating the mixture to at least a
reaction temperature that is sufficient to create a substantially
fused layer of nanosized particles.
11. The method of claim 10, wherein the resulting layer comprises
chalcopyrite.
12. The method of claim 10, wherein a substantial portion of the
metal alloy nanoparticles are less than 50 nm.
13. The method of claim 10, wherein the resulting layer is suitable
for use in a photovoltaic cell.
14. The method of claim 10, wherein the heating step comprises
heating the mixture to a temperature of at least 250.degree. C.
15. The method of claim 10, wherein the resulting layer is less
than about 1 micron.
16. The method of claim 10, wherein the resulting layer is less
than about 500 nanometers.
17. The method of claim 10, wherein the resulting layer is less
than about 500 nanometers on average.
18. A composition having photon-absorbing characteristics, the
composition comprising metal alloy nanoparticles made from a vapor
condensation process, the composition suitable for use in an
electronic device.
19. The composition of claim 18, wherein the metal alloy
nanoparticles are comprised of at least one metal from group IB,
IIB, or IIIA.
20. The composition of claim 19, wherein the metal alloy
nanoparticles comprises at least one of copper, indium, or
gallium.
21. The composition of claim 18, wherein a substantial portion of
the metal alloy nanoparticles is less than 50 nm.
22. The composition of claim 18, wherein at least some of the metal
alloy nanoparticles have an oxide shell.
23. The composition of claim 18, wherein the metal alloy
nanoparticles have sufficiently high reactivity to permit reaction
with material from either Group VA and/or VIA in the gas, liquid,
or solid state.
24. The composition of claim 23, wherein the material comprises
either elemental selenium and/or sulfur.
25. A photovoltaic cell comprising: a photon-absorbing layer
comprising copper-indium alloy nanoparticles substantially fused
together, said layer prepared by heating the nanoparticles
sufficiently to permit reaction with material comprising either
Group VA and/or VIA; an electrically conductive substrate
supporting the photon-absorbing layer and providing at least a
portion of an electrical circuit in combination with said layer; an
emitting layer comprising material capable of absorbing electrons
from the photon-absorbing layer; and an anti-reflective coating
comprising material suitable for permitting a significant amount of
sunlight that strikes the cell to reach the photon-absorbing
layer.
26. The photovoltaic cell of claim 25, wherein the photon-absorbing
layer is less than about 0.5 microns thick.
27. The photovoltaic cell of claim 25, further comprising an
environmental protection layer to reduce environmental degradation
of the cell during use.
28. The photovoltaic cell of claim 25 wherein the Group. VA and/or
VIA material comprises either selenium and/or sulfur.
29. The photovoltaic cell of claim 25 wherein the photon-absorbing
layer further comprises gallium.
30. The photovoltaic cell of claim 25 wherein the anti-reflective
coating comprises zinc oxide.
31. The photovoltaic cell of claim 25 wherein the emitting layer
comprises cadmium sulfide.
32. The photovoltaic cell of claim 25 wherein the environmental
protection layer further comprises glass having a low iron
content.
33. A stratified layer of metal alloy nanoparticles comprising the
formula Cu.sub.1In.sub.1-xGa.sub.x.
34. The layer of claim 33, wherein the gallium concentration in at
least one of the stratifications is different from the gallium
concentration in another stratification.
35. The composition of claim 33, wherein x ranges from 0 to 1.
36. The composition of claim 33, wherein the concentration of
gallium is lower proximal to the emitting layer.
37. The composition of claim 33, wherein there are a minimum of
three stratifications and a maximum of twenty stratifications.
38. The layer of claim 33, wherein the thickness is less than about
1 micron.
39. The layer of claim 33, wherein the average thickness is less
than about 500 nanometers.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The inventions disclosed herein relate generally to the
manufacture of materials for thin film photovoltaic cells. More
specifically, the invention relates to an improved production
process for making the active absorbing material containing metal
alloy nanoparticles that allows for increased efficiency, reduced
cost, and reduced weight.
[0003] 2. Related Art
[0004] A photovoltaic cell is a device that converts light energy
directly into electricity. The high cost of polysilicon and
resultant high cost of silicon solar cells has prevented widespread
use of solar energy. Recent advances in low cost, high efficiency,
thin film polycrystalline solar cells based on
copper-indium-gallium-selenium-sulfide (CIGS) absorption layers
promises to make solar energy competitive with energy derived from
fossil fuels. Although these materials have some of the highest
efficiencies of all classes of solar cells, exceeding 15%, several
steps in the production process of CIGS solar cells are toxic
and/or expensive. Additionally, with thicker active CIGS layers in
a photovoltaic device, there is an increase chanced of layer
defects that could lower overall cell efficiency.
[0005] These limitations present a roadblock to safe and
cost-efficient mass-manufacture. The present invention is helpful
in overcoming at least some of these deficiencies. For example,
preparing a layer with reduced thickness is one key aspect to
improve photovoltaic efficiency and to reduce materials cost. An
additional benefit to using a thinner CIGS layer is a decreased
weight contribution, which is critical in space applications.
SUMMARY OF THE INVENTION
[0006] In some embodiments of the current invention, a photovoltaic
cell has been prepared incorporating a photon-absorbing layer on an
electrically conductive substrate in which the photon absorbing
layer is comprised of metal alloy nanoparticles having the formula,
for example, Cu.sub.1In.sub.1-xGa.sub.x, where x equals from 0 to
1. In an inventive method of manufacture, the metal alloy
nanoparticles are heated on the substrate in the presence of
elements such as, for example, selenium and/or sulfur to a
temperature sufficiently high to permit reaction, and preferably,
become fused together to form a thin layer on the electrically
conductive substrate to provide at least a portion of an electrical
circuit that permits the flow of electrons. Preferably, this layer
is less than 1 micron in thickness and, more preferably, the layer
is less than about 500 nanometers.
[0007] In accordance with at least one of the preferred embodiments
disclosed herein, a copper-indium-gallium (CIG) alloy was prepared
utilizing facile manufacturing conditions. For example, but without
limitation, copper-indium-gallium alloy can be selenized and/or
sulfidized with elemental selenium and/or sulfur to form a
photon-absorbing material, where by the resulting layer has a
thickness of no more than about 1 micron, but preferably much less
than 1 micron.
[0008] At least some of the embodiments of the present invention
benefit from the presence of an increased number of reactive atoms
exist at the surface of a nanoparticle. As such, metal alloy
nanoparticles and their oxides can be utilized for further alloying
under favorable reaction conditions. Metal alloy nanoparticles used
in the described method in the preferred embodiments are from
groups IB, IIB, or IIIA on the periodic table have a diameter of
less than 50 nm. More preferably, the metal alloy nanoparticles are
comprised of copper and indium, and most preferably
copper-indium-gallium (CIG).
[0009] In at least one embodiment of the present invention, a
photovoltaic device comprises an emitting layer is applied to the
photon-absorbing layer. Preferably, the emitting layer is comprised
of a material that is highly efficient at electron transport from
the photon-absorbing layer, and most preferably comprises cadmium
sulfide or similar molecule. On top of the emitting layer, an
anti-reflective coating may be applied. In some of the preferred
embodiments, the anti-reflective coating is both optically and
electrically conductive to permit sunlight to reach the emitting
layer effectively. The anti-reflective coating may preferably be
zinc oxide.
[0010] In other preferred embodiments, an environmental protection
layer is provided to provide weather-resistant properties to the
device. Preferably, the environmental protection layer has optical
and electrical conductive property, and may preferably comprise
low-iron glass.
[0011] In one application of the present inventive process, a
method of preparing a photon-absorbing layer of nanosized material
is contemplated. One such method comprises heating metal alloy
nanoparticles, prepared for example from a vapor condensation
process, with at least one element selected from Groups VA and/or
VIA on an electrically conductive substrate. Preferably, the
nanosized material in the photon-absorbing layer is prepared by a
vapor condensation process. An example of such a process is
described in U.S. Pat. No. ______ [Ser. No. 10/840,109], which is
incorporated herein in its entirety by reference. Other methods for
obtaining beneficial photon-absorbing layers for use in effective
photovoltaic devices may be employed. The composition is heated
sufficiently high to permit reaction and create a substantially
fused layer of nanosized particles. More preferably, the resulting
layer is photon-absorbing for effective use in a photovoltaic
device, and may comprise chalcopyrite.
[0012] In addition, it is preferable that a substantial portion of
the metal alloy nanoparticles used in the method are less than 100
nm, and most preferably less than 50 nm. Utilization of the
preferred particle size increases uniformity of the resulting layer
after the heating step.
[0013] During the heating step, it is preferred that the mixture be
heated to a temperature such that there is sufficient reaction
between the metal alloy nanoparticles and at least one element
selected from groups VA and/or VIA. Most preferably, the
temperature should be at least 250.degree. C.
[0014] In some of the embodiments, the temperature must be
sufficient form a substantially fused layer of nanoparticles. It is
more preferable that the layer be uniform and thin, most preferably
less than 500 nm in thickness.
[0015] Some of the preferred embodiments detail the composition of
a photovoltaic absorbing chalcopyrite material prepared from metal
alloy nanoparticles. Preferably, the nano-scale metal alloy
particles are comprised of at least copper and indium, and more
preferably copper, indium, and gallium.
[0016] According to some of the embodiments in the current
invention, a composition comprising metal alloy nanoparticles
prepared from a vapor condensation process can be prepared for use
in an electronic device. The metal alloy nanoparticles are
preferably comprised from at least one metal from Groups IB, IIB,
and/or IIIA, and arc most preferably at least one of copper,
indium, and/or gallium.
[0017] Preferably, the metal alloy nanoparticles should have
sufficiently high reactivity to permit reaction with elements from
either Group VA and/or VIA in the gas, most preferably with
selenium and/or sulfur in the liquid, or solid state. Thus, to
permit this reaction, the particles should have a size of less than
100 nm, and most preferably less than 50 nm. At least some of the
metal alloy nanoparticles have an oxide shell.
[0018] In other preferred embodiments, a photovoltaic cell
comprising a photon-absorbing layer, electronically conductive
substrate, emitting layer, and anti-reflective coating is
described. The photon-absorbing layer is preferably comprised of
copper-indium nanoparticles, and most preferably comprised of
copper-indium-gallium nanoparticles. The nanoparticles are
substantially fused together, prepared by heating metal alloy
nanoparticles sufficiently to permit reaction preferably with
material from either Group VA and/or VIA, and most preferably with
selenium and/or sulfur.
[0019] The photon-absorbing layer is supported on an electronically
conductive substrate which provides a portion of an electrical
circuit in combination with the photon-absorbing layer. Preferably,
this layer is thin and continuous, and most preferably less than
500 nm thick.
[0020] An emitting layer is applied directly to the
photon-absorbing layer. Preferably, the emitting layer is comprised
of a material that is highly efficient at electron transport from
the photon-absorbing layer, most preferably cadmium sulfide. An
anti-reflective coating is applied directly to the emitting layer.
Preferably, an anti-reflective coating is both optically and
electrically conductive to permit sunlight to enter the emitting
layer, and most preferably is zinc oxide.
[0021] Additionally, the composition may also comprise an
environmental protection layer. Preferably, this layer is comprised
of material that reduces damage cause by weathering, and is most
preferably composed of low-iron glass.
[0022] Some of the preferred embodiments detail stratified layers
of metal alloy nanoparticles, comprising the formula
Cu.sub.1In.sub.1-xGa.sub.x, wherein x can vary from 0 to 1.
Preferably, the gallium concentration in at least one of the
stratifications is different from the gallium concentration in
another stratification, and most preferably the concentration of
gallium is lower proximal to the emitting layer.
[0023] At least some of the preferred embodiments describe at least
three and up to twenty stratifications. The layer thickness of all
stratifications combined should be thin and continuous, preferably
the combined thickness is less than one micron, and most preferably
less than 500 nm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The features mentioned above in the summary of the
invention, along with other features of the inventions disclosed
herein, are described below with reference to the drawings of the
preferred embodiments. The illustrated embodiments in the figures
listed below are intended to illustrate, but not to limit the
inventions.
[0025] FIG. 1 is a schematic of a thin film solar cell described in
some of the embodiments.
DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS
[0026] The features mentioned above in the summary of the
invention, along with other features of the inventions disclosed
herein, are described below with reference to the drawings of the
preferred embodiments. The illustrated embodiments in the figures
listed below are intended to illustrate, but not to limit the
inventions.
[0027] A photovoltaic (PV) cell is a device that converts solar
energy directly into electricity. While there are several different
classes of solar cells, the present invention has particular but
not exclusive applicability to thin film solar cells made from
materials such as copper-indium-gallium diselenide (CIGS) or
copper-indium-gallium-selenium sulfide (CIGSS). Unlike traditional
Si-based solar cells, CIGS and CIGSS cells are flexible and are
more acceptable for a wider variety of surface profiles, such as
curved or contoured surfaces. The diagram in FIG. 1 shows at least
some of the different layers in, for example, a CIGS- or
CIGSS-based solar cell. Base material 101 may be glass or metal
foil, although a material having some plastic and/or elastic
characteristic is preferable so that the cells permit increased
flexibility. Upon the base material, substrate foil 102 may be
deposited and can be used as a back contact. The substrate foil 102
is preferably a metal foil and may preferably comprise molybdenum.
A photon-absorbing CIGS or CIGSS layer 103 may then be deposited
onto foil 102. The thickness of this layer is highly dependent on
how CIGS is applied to the surface. While the thickness of a
typical CIGS cell is about two or so microns, the present inventive
photon-absorbing layer 103 has an average thickness of less than
one micron and preferably less than about 500 nm on average and
most preferably a maximum thickness of about 500 nanometers. The
CIGS layer is preferably formed as a p-type, photon-absorbing,
layer based upon the particular arrangement of copper, indium, and
gallium atoms.
[0028] To enhance the flow of electrons through the cell, an n-type
electron transporting emission layer 104 can be applied to the
photon-absorbing layer 103, preferably a layer comprising cadmium
sulfide. An anti-reflective coating of zinc oxide 105 may be
applied to the emission layer 104. Preferably, the anti-reflective
layer is both electrically and optically conductive, allowing
photons to reach the photon-absorbing layer 103. Electrical contact
106 may be applied to complete circuit 107 with foil 102 to collect
and use the energy gained from light absorption. If desired, an
environmental protection layer 108 may be placed on top the
anti-reflective coating 106 and electrical contact 105 to minimize
the effects of weathering of the photovoltaic device.
[0029] The present invention benefits from increased surface area
of the reactive metal alloy nanoparticles, as compared to the
surface area of the metal substrate particles, primarily due to the
large number of atoms on the surface of the nanoparticles. As an
example, a cube comprising a plurality of three nanometer nickel
particles considered essentially as tiny spheres. As such, they
would have about ten atoms on each side, about one thousand atoms
in total. Of those thousand atoms, 488 atoms would be on the
exterior surface and 512 atoms on the interior of the particle.
This means that roughly half of the nanoparticles would have the
energy of the bulk material and half would have higher energy due
to the absence of neighboring atoms (nickel atoms in the bulk
material have about twelve nearest neighbors while those on the
surface has nine or fewer). A three micron sphere of nickel would
have 10,000 atoms along each side for a total of one trillion
atoms. There would be 999.4 billion of those atoms in the bulk (low
energy interior) material. That means that only 0.06% of the atoms
would be on the surface of the three micron-sized material compared
to the 48.8% of the atoms at the surface of the three nanometer
nickel particles.
[0030] Depending upon the process of manufacture, the metal alloy
nanoparticles can be configured to have a surface energy
sufficiently high to react with other elements under benign
reaction conditions. For example, micron sized
copper-indium-gallium (CIG) alloy particles have a lower surface
energy density and would not react with elemental selenium or
sulfur at temperatures below 750.degree. C. Typically, highly
reactive and toxic H.sub.2Se or H.sub.2S gasses would be necessary
to complete this reaction. However, CIG alloy nanoparticles,
including those as small as 50 nanometers, can react with elemental
materials such as selenium and/or sulfur at 250.degree. C. to
produce CIGS or CIGSS, both photon-absorbing materials. As such,
metal alloy nanoparticles have been shown to have exponentially
higher surface area-to-volume ratio than that of a micron-scale
metal alloy particle. Thus, CIGS or CIGSS material can be produced
under more gentle, environmentally friendly conditions by virtue of
the increased reactivity of nanoscale CIG. Layers comprising CIGS
and CIGSS materials may form chalcopyrites.
[0031] When the CIG metal alloy nanoparticles are heated in the
presence of selenium and/or sulfur on the conductive substrate, the
materials combine to form a CIGS or CIGSS photon-absorbing layer.
The resulting nanoparticles become partially fused or "necked".
Although the layer is uniform and continuous, the nanoparticles
largely retain their discrete size and shape, and thus high surface
area.
[0032] Photovoltaic cell efficiency is highly dependent on the
cell's ability to efficiently absorb photons and transmit
electrons. In some cases, poor efficiency is caused by layer
defects in CIGS or CIGSS photon absorbing material formed during
the heating process and non-uniform distribution of material.
Although thicker layers have the potential to absorb more photons,
they are also more susceptible to these defects. However, when a
highly active, thin, defect-free layer is applied, efficiency is
highest. To optimize PV efficiency, the photovoltaic absorbing
layer should be as thin as possible to decrease the likelihood of
defects in the layer. Thus, another aspect of at least one of the
embodiments includes the idea that by using metal alloy
nanoparticles as the starting materials, there is greater control
over layer thickness and the potential to produce a thin layer,
less than 500 nm in thickness.
[0033] The reactive metal alloy nanoparticles are preferably formed
by a vapor condensation process such as that described in U.S. Pat.
No. ______ [Ser. No. 10/840,109], the entire contents of which is
hereby expressly incorporated by reference. With such a process,
material may be fed onto a heater element so as to vaporize the
material, allowing the material vapor to flow upwardly from the
heater element in a controlled substantially laminar manner under
free convection, injecting a flow of cooling gas upwardly from a
position below the heater element, preferably parallel to and into
contact with the upward flow of the vaporized material and at the
same velocity as the vaporized material, allowing the cooling gas
and vaporized material to rise and mix sufficiently long enough to
allow nano-scale particles of the material to condense out of the
vapor, and drawing the mixed flow of cooling gas and nano-scale
particles with a vacuum into a storage chamber. Binary, tertiary,
or ternary metal nanoparticle alloys of Groups IB, IIB and/or
Groups IIIA on the periodic table preferably have a particle size
of less than 50 nanometers, and can be so more reliably when
prepared by a vapor condensation process.
[0034] For further efficiency optimization, the band gap energy of
the photovoltaic absorbing layer can be modified by stratifying the
amount of gallium, where a higher gallium concentration is located
closer to the substrate and a lower concentration closer to the
photon-absorbing and emission layer interfact (p-n junction). This
can be accomplished via multiple layers of nano-scale metal alloy
particles with a different gallium concentration in each layer. By
applying these layers with subsequent selenization and
sulfidization, a graded absorber layer is produced, and the sum of
all layers in still less than 0.5 microns in thickness. This
methodology has an added benefit in that surface contact is
enhanced at the p-n junction, as cadmium sulfide and gallium repel
each other. An example also shown in FIG. 1. Base material 101 is
typically glass or metal foil, however plastic is most preferable
so that the cells have increased flexibility. Upon the base
material, substrate foil 102 is deposited and used as a back
contact, and is preferably a metal foil and most preferably
molybdenum. First, gallium-rich CIG layer 111 is then deposited
onto foil 102. Subsequent CIG layers are then deposited, each with
decreased gallium concentration. A final, gallium-free layer 112 is
applied. The total sum of layers 113 has a maximum thickness of 500
nm. These deposited layers are then heated and then reacted with
elements from Group VA and/or IVA. To permit the flow of electrons
through the cell, an n-type electron transporting cadmium sulfide
emission layer 104 is then applied on top of photon-absorbing
layers 113. An anti-reflective coating of zinc oxide 105 is applied
on top of emission layer 104. This layer is both electrically and
optically conductive, allowing photons to reach photon-absorbing
layers 113. Electrical contact 106 is applied to complete circuit
107 with foil 102 to collect and use the energy gained from light
absorption. Furthermore, an environmental protection layer is
placed on top of anti-reflective coating 108 and electrical contact
106 to prevent and protect against weathering.
EXAMPLE
Preparation of CIGS
[0035] Copper (19.278 g), indium (80.36 g), and gallium (20.916 g)
were mixed in a graphite crucible under argon at 800.degree. C.,
stirred to mix, and allowed to cool. The resulting ingot was
crushed into a powder. This powder was further reacted in a vapor
condensation reactor at 1400.degree. C. for one hour to yield
copper-indium-gallium alloy nanoscale particles, with a final
composition of Cu.sub.1In.sub.0.7Ga.sub.0.3. A portion of the
resulting nanoscale alloy (0.778 g) was placed in a graphite
crucible and selenium (0.898 g) was added. The crucible was covered
with a graphite lid, then placed in an oven and heated to
500.degree. C. for 75 minutes in an inert atmosphere. The resulting
CIGS photovoltaic absorber material was allowed to cool to room
temperature.
[0036] The foregoing description is that of preferred embodiments
having certain features, aspects, and advantages in accordance with
the present inventions. Various changes and modifications also may
be made to the above-described embodiments without departing from
the spirit and scope of the inventions.
* * * * *